Hydra vulgaris Opening its Mouth (1 of 2) (video) Cell Press Share Print E-Mail Loading video... Caption Hydra vulgaris is opening its mouth. Scale bar = 200 micrometers. Credit Carter and Hyland et al/Biophysical Journal 2016 Usage Restrictions Credit Required. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.